1. Technical Field
The subject invention relates to a fluid pumping assembly of the type having a variable displacement capacity and more specifically to a wobble plate type pumping assembly wherein the position of the wobble plate within the housing and the angulartory movement of the wobble plate is positively controlled to precisely control the displacement of the pump.
2. Description Of The Prior Art
Wobble plate type pumping assemblies having variable displacement capabilities are well known in the prior art. In these types of pumping assemblies, the position of the wobble plate in the pump housing is adjusted to vary the displacement of the pump. Varying the displacement in wobble plate type pumps can be achieved in a number of ways. For example, U.S. Pat. No. 4,428,718 issued to Skinner on Jan. 31, 1984 discloses a compressor which employs a control valve to vary the displacement of the compressor. Control valves of this type are typically disposed in the discharge and suction chambers of the compressor and react to various pressure differentials to control the crank case pressure to increase or decrease the wobble plate angle relative to a drive shaft, thus varying the capacity of the compressor or pump.
Other examples can be found in pumps wherein the wobble plate is mounted about a centrally disposed rotating or driven shaft wherein the rotating shaft is adjustable within the pump housing to vary the displacement. Prior art disclosing such structure can be found in U.S. Pat. No. 4,433,596 issued to Scalzo on Feb. 28, 1984; U.S. Pat. No. 4,077,269 issued to Hodgkinson on Mar. 7, 1978 and U.S. Pat. No. 2,964,234 issued to Loomis III on Dec. 13, 1960.
However there are certain disadvantages which are inherent in the prior art. For example, pumps which employ control valves, such as the Skinner '718 patent noted above, are totally dependent upon compressor crank case pressure. As such, these types of compressors are not responsive to changes in other important parameters such as engine load or engine RPM.
Pump assemblies having wobble plates mounted about power driven rotating shafts which are also adjustable within the pump housing must employ complex structure in order to achieve the variable displacement feature. This results in an increase in the cost of manufacturing these pumps as well as the increase probabilities for failure of one of the multiple moving parts.
The prior art is further deficient in that the position of the wobble plate and thus the pump displacement cannot be precisely controlled. The displacement may be merely increased or decreased but not precisely controlled to a predetermined level. Furthermore, it is not possible in the prior art to precisely maintain the displacement of the pump over time. Accordingly, pumping assemblies, such as refrigerant compressors in automotive applications, which are driven via a power input through a pulley must also include a clutch assembly which is able to disengage the compressor when no output is required or during heavy engine loading.